In the completion of oil and gas wells, after drilling to the desired depth, production casing is run into the drilled well bore and is set in place by cementing the annulus between the casing and the well bore. This cementing step is normally accomplished by setting a cement retainer at a desired depth and by pumping cement, at high pressures, below the cement retainer. The retainer prevents the movement of cement into the interior of the casing thereby forcing the cement into the annulus between the casing and the well bore.
The customary procedure for completing such a cementing process includes running the cement retainer into the well, and setting the retainer using either a mechanical or hydraulic setting tool. If the setting procedure is hydraulic, the tool is run into the well on the end of a pipe string, and once set, the cement retainer setting tool is uncoupled from the cement retainer and it, with the pipe string, is removed from the well. The pipe string is then reinserted into the well and cement is pumped therethrough to complete the cementing operation.
Thus, the process of setting the cement retainer, when set hydraulically, requires that the pipe string be run into the well, then backed out, and then rerun to complete the cementing operation. Such procedure takes substantial time and manpower, with the investment being multiplied as the depth of the well increases. Thus, tools and procedures for eliminating the time and manpower needed to complete the cementing process represent a substantial advancement in the art.
Once set, the cement retainer is removed by drilling through it. Thus, it is critical that a cement retainer setting tool not permit premature setting as is possible in many current designs. The tool must also provide for ease in setting the tool at the desired time. Further, the sequence of steps which must be accomplished by the operator in setting the tool must be straight forward and not require any interpretation of downhold pressure or sequences, which may be difficult or impossible to ascertain by the operator.
Retainer setting tools are normally reused many times. Prior to such reuse, however, the tools must be disassembled and shear pins and other components redressed. In some current retainer setting tools, fluids under high pressures may be trapped within the tool when down hole. When such tools are redressed, these pressurized fluids will be released resulting in the possibility of injury. Thus, the simplicity and safety with which the tool can be redressed is of significant importance.